Metallographic study on Nd-Fe-Co-B sintered magnets

Metallographic study has been carried out on the Nd-Fe-Co-B alloys to clarify the change in coercivity with the Co composition substituted for Fe in the Nd
2
Fe
14
B type sintered magnets. The decrease in coercivity caused by the Co substitution is attributed to the formation of soft-magnetic phases such as Nd(Fe, Co)
2
and Nd(Fe, Co)
3
. The mole ratio of Nd to (Fe+Co) of these soft-magnetic phases decreases with increasing the Co substitution. The Co concentration is much higher in these soft-magnetic phases than in Nd
2
(Fe, Co)
14
B matrix. The A1 addition in Nd-Fe-Co-B magnet makes the Nd(Fe, Co)
2
compound unstable to form the non-magnetic Nd
3
(Fe, Co, Al) compound, resulting in the increase in the coercivity of Nd-Fe-Co-B magnet.